Power interruptions are defined as short term or long term loss of electrical power. The production of power is based upon an infrastructure that is reliable but quite complex. Power plants such as nuclear, natural gas, coal, hydroelectric, wind, solar and the like are used to generate electrical power. The electrical power can be transported over long distances by use of transmission lines that may be 138,000 volts or higher which are directed to substations for redistribution. Transmission lines typically consist of three cables (2 ‘hot’ and one defining the ‘ground’ in a 3-phase system) which are suspended from tall towers and exposed to the elements. Transmission supply cables terminate at regional power stations and substations where the high voltages are converted into lower voltages ranging from 13,800 volts to 69,000 volts. This electricity is then transmitted into cities, towns, and neighborhoods either atop local telephone poles or by use of underground wiring. Localized power is provided by a transformer that steps voltage down to 220 volts supplying individual and commercial premises.
The above description illustrates a textbook power distribution wherein the end consumer receives unlimited and uninterrupted power. However, in reality power interruptions can be caused at any time from countless situations. For instance, power interruption may be caused by faults at the power stations, substations, transmission lines and/or distribution connectors, short circuits, overloading, storms, and so forth. A vehicle striking a power pole can result in power interruption. New York City is notorious for its underground electrical cable fires. Transmission lines are aging and in critical need of replacement but the extensive network are so enormous that it cannot be logistically or affordable corrected. The loss of power, even momentary, can cause air conditioning systems to shut down. Even a transient fault, a momentary loss of power is caused by a temporary fault, can be sufficient to disable an air conditioning system. When power is restored the voltage may fluctuate causing the transient fault and most air conditioning systems cannot accept an instant restart resulting in a lock condition.
A voltage fluctuation also known as a brownout takes place when there is a voltage drop in an electrical power supply. A brownout may cause voltage to fluctuate causing the transient fault and again most air conditioning systems cannot accept an instant restart resulting in a lock condition.
In the operation of an air conditioning compressor, once power is interrupted to the compressor it is desirable and in some instances mandatory to keep the compressor off for a period of time. If a compressor is powered off momentarily and immediately restarted, the compressor will have to start up against a high head pressure within the system. To overcome the high head pressure, a large amount of current is passed through the motor windings which can immediately overheat the motor causing a premature fault. For instance, a conventional air conditioner employs a compressor motor that includes a thermal overload switch. When the windings in the motor overheat, the thermal overload switch opens to shut the motor off. Once the windings begin to cool down, the thermal switch resets and the motor is allowed to restart. However, if the high head pressure remains then the motor will trip again and either the thermal switch must be manually reset or the thermal switch must be tricked into cycling between the on and off states. As a result, the momentary power loss can result in a tremendous strain placed on the motor which severely shortens the life of the motor.
This problem is further made problematic in community shared air conditioning systems. For instance, buildings rely upon air conditioners that are water-cooled by use of a cooling tower. Should the flow of water stop for any reason the compressor located in the individual units is forced into a hard lock out. Thus, even if power is maintained to the compressor, the system cannot operate until the power is disconnected from the compressor to allow a reset. In a water-cooled air conditioner, the heat in the Freon gas is discharged into water that is recirculated back to externally mounted water cooler. Should the recirculation pump fail, or the water flow discontinued for any reason, the compression will go into a hard lock out. If the high pressure limit is tripped, the system must cool down and the pressure reduced before restarting. If a restart occurs improperly, the compressor motor will heat up and the above mentioned thermal switch will also require a reset.
There exist many locations wherein even a temporary power interruption can lead to long term consequences. Use of air conditioners in high-rise buildings present a particular problem wherein the building windows do not open and the resident may be absent for long periods of time. The most prominent example of this would be condominiums found in south Florida where winter residents vacant the premises for long periods of time, commonly during the tropical summer months when the heat and humidity remains the highest. Loss of air conditioning in a structure can quickly lead to mold and mildew damage. Should excess water enter the structure, an air conditioner is capable of dehumidifying the air which eliminates excess moisture from becoming a major problem.
A basic solution to the above problem is to employ a maintenance individual to check every structure that is vacant on a daily basis. If the air conditioner unit is shut off due to a power interruption, or in a hard lock out due to the failure of cooling water, a maintenance man can simply restart the system. However, the labor cost of checking every residence on a daily basis can be cost prohibitive. In addition, opening up a residence for inspection causes security concerns.
Other known solutions to power interruptions that caused faults with air conditioners is to include the use of a minimum off-timer in the control circuit of the compressor motor. An interruption in current flow in the motor windings resulting from a power interruption causes the minimum off-time delay circuit to keep the starter relay or contactor, which activates the compressor motor, in a turned off state for a predetermined period of time after the loss of power. By maintaining the compressor motor in an off state for a fixed minimum time period after a power interruption, pressure in the compressor is allowed to stabilize, thereby preventing the motor from overloading when power is reapplied to the system. Although these circuits have been successful in protecting compressor motors, the cost of installing the devices into the control circuits of the systems is relatively high. However, such devices to not address the problems associated with lack of cooling water and the associated hard lock out.
U.S. Pat. No. 3,054,271 discloses an air conditioning control means connecting a circuit and motor for starting and stopping the motor in response to predetermined load conditions. The device includes a timing means in the supply circuit electrically actuated in response to any stopping of the motor to open the supply circuit to preclude restarting of the motor for a predetermined time of constant duration subsequent to each stoppage of the motor.
U.S. Pat. No. 3,785,165 discloses a thermostatic air conditioner control for use with individual unit air conditioners having a thermostatic switch disposed at a location remote from the air conditioner. The control includes circuitry interposed between the air conditioner and a source of electrical energy operative a selected time interval after closure of the thermostatic switch to energize a socket in which the air conditioner is plugged, and operative a selected time interval after opening of said thermostatic switch to de-energize the socket.
U.S. Pat. No. 4,939,909 discloses an air-conditioner with a refrigerating circuit. An electric current path for making a current flow through a compressor includes an AC power source, to which a current transformer is coupled, and an output of the current transformer is converted into a DC voltage which is then given as a (+) input of a comparator. A reference voltage is given to a (−) input of the comparator. When the DC voltage exceeds the reference voltage of the comparator, the high level is outputted from the comparator. When the high-level output from the comparator persists for three seconds, the compressor is stopped forcedly and a three-minute timer is turned on. After a lapse of three minutes, the flow of the current through the current path of the compressor is resumed. Thereby, a lightly locked state is removed. If the output of the comparator still remains at the high level when the energizing is resumed, the compressor is put in the stopped state again. When such stopping and resuming of energizing of the compressor are repeated four times, the energizing of the compressor is stopped assuming that the compressor is in a heavily locked state.
U.S. Pat. No. 5,524,448 discloses a minimum off-time device that delays the restart of a compressor motor of a refrigeration system after power provided to the motor has been interrupted. The minimum off-time device is a standalone unit that is located outside the refrigeration system. The device is retrofitted to the refrigeration system by simply plugging the power line of the system into the device, which is then plugged into an AC wall receptacle, or alternatively, the device can be connected between the power line of the refrigeration system and an electrical circuit breaker panel. The minimum off-time device normally allows power from the AC power source to reach the refrigeration system. However, when a power interruption occurs at the AC power source, and subsequently, power is reapplied, the minimum off-time delay device immediately disconnects the refrigeration system from the AC power source and begins a timing sequence. When the timing sequence ends after a predetermined period of time passes, the minimum off-time device reconnects the refrigeration system to the AC power source.
EP498645B1 discloses a controller for a refrigerator to prevent a voltage drop in the power supply occurring when AC power is supplied to a large number of air conditioners from the same power source simultaneously such as when a power failure is recovered to normal. The controller comprises a time setting circuit to arbitrarily set the timing of a reset signal applied to a microprocessor. A time setting switch to an arbitrary value, the time elapse from the generation of the reset signal to the activation of the compressor. According to the setting of the time setting switch, the microprocessor controls the delay time for starting the air conditioner. When the power supply is restored after power failure, it is possible to prevent the air conditioners from restarting simultaneously and thus prevent a voltage drop in the power supply.
Thus, what is lacking in the industry is a low-cost, maintenance free power interruption device that can be installed without affecting the control circuitry of the air conditioning system and provides a timed reset the system at least once per day.